1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly, to a nanocrystalline superlattice silicon (Si)-silicon dioxide SiO2 electroluminescence (EL) device and light-emitting diode (LED) device.
2. Description of the Related Art
An early paper in the field, published in Nature (440–444, 2000) by L. Pavesi, deals with silicon quantum dots. Since 2000, there have been numerous reports of optical gain in waveguide structures, EL, and light-emitting diode (LED) applications containing silicon quantum dots in the 2 to 4 nanometer (nm) range, prepared by different techniques. However, there are inconsistencies between the various experimental reports, and theoretical studies have not conclusively identified the mechanisms for optical gain.
Many researchers have recently reported on the EL properties of Si rich silicon oxides. Keisuke Sato, from Tokyo Denki University, presented an interesting paper dealing with electroluminescence from Si-rich silicon oxide. To make the Si-rich silicon oxide thin films, he bonded small (5×5 mm) silicon pieces on a silicon dioxide target. Using radio frequency (RF) sputtering, a Si-rich silicon oxide, with silicon nano-particles of a size around 2.5 nm, was formed. The surface of Si rich silicon oxide was etched by HF and then post-annealed. Both the HF surface etching and the temperature of the post-annealing were reported to be key factors associated with the color of light emission. Red emission color was obtained from the HF treatment sample. Green emission color was observed from the sample post-annealed at 600° C., and blue for the sample post-annealed at a temperature of 900° C. From I–V measurements, Sato gave the light emission threshold voltages: 4.0V for red emission, 9.0V for green and 9.5V for blue emission. This data suggests very promising Si quantum dots EL and LED applications.
Another interesting work comes from STMicroelectronics, Italy. Dr. Maria E. Castagna et al. presented a paper entitled “High efficiency light emission devices in silicon.” at the 2003 MRS spring meeting. The reported device consists of MOS structures with erbium (Er) implanted in the gate oxide. The device exhibited strong 1.54 μm (micrometer) electroluminescence at 300° k (room temperature) with a 10% external quantum efficiency, comparable to that of standard light emitting diodes using group III–V semiconductors. Emissions at different wavelengths have been achieved incorporating different rare earths (Ce, Tb, Yb, Pr) in the gate dielectric. The external quantum efficiency depends on the rare earth ions incorporated, and ranges from 10% (for a Tb doped MOS) to 0.1% (for an Yb doped MOS). Much more stable light emitting MOS devices have been fabricated using Er-doped SRO (Si-rich silicon oxide) films as the gate dielectric, but the external quantum efficiency is reduced to 0.2%. With respect to the light emission mechanism, it is thought that Er pumping occurs partly due to the impact of hot electrons, and partly by energy transfer from the Si nanostructures to the rare earth ions, depending on the Si excess in the film.
Dr. Pasquarello has proposed a theory for the photoemission associated with a Si—SiO2 interface. According to the theory, Si 2p core-level shifts occur at the Si(001)—SiO2, and depend linearly on nearest-neighbor oxygen atoms. Second nearest-neighbor effects turn out to be negligibly small. Therefore, an efficient photoemission spectra requires that all Si oxidation states be present at the interface. Based on this theory, the making of a high density Si—SiO2 interface is a critical issue for EL device applications.
It would be advantageous if a more efficient, easy to fabricate, EL device could be made based upon a high density Si—SiO2 interface.
It would be advantageous the density of a Si—SiO2 interface could be increased by using a multi-layer Si—SiO2 superlattice.